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PDF RT8058 Data sheet ( Hoja de datos )
| Número de pieza | RT8058 | |
| Descripción | High Efficiency PWM Step-Down DC/DC Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RT8058 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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Preliminary
RT8058
1MHz, 2A, High Efficiency PWM Step-Down DC/DC Converter
General Description
The RT8058 is a current mode PWM step-down converter.
The chip is ideal for fixed frequency and low ripple
applications over full range of load conditions. Its input
voltage range is from 2.6V to 5.5V with a constant 1MHz
switching frequency that allows it to adopt tiny, low cost
www.DataSchaepeat4cUit.ocrosmand inductors with 2mm or less in height making
it ideal for single-cell Li-lon/polymer battery applications.
The low on resistance internal MOSFET can achieve high
efficiency without the need of external schottky diodes in
wide operating ranges and the output voltage is adjustable
from 0.6V to 5V that can provide up to 2A load current.
The RT8058 operates at 100% duty cycle for low dropout
operation that extends battery life in portable devices.
The RT8058 is available in a WQFN-16L 3x3 package.
Ordering Information
RT8058
Package Type
QW : WQFN-16L 3x3 (W-Type)
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial Standard)
Note :
Richtek Pb-free and Green products are :
}RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
}Suitable for use in SnPb or Pb-free soldering processes.
}100% matte tin (Sn) plating.
Features
l 0.6V Reference Allows Low Output Voltage
l Low Dropout Operation : 100% Duty Cycle
l 2A Load Current
l < 2uA Shutdown Current
l Up to 95% Efficiency
l No Schottky Diode Required
l 1MHZ Constant Switching Frequency
l Low RDS(ON) Internal Switches
l Internally Compensated
l Internal Soft-Start
l Over temperature Protection
l Short Circuit Protection
l Small 16-Lead WQFN Package
l RoHS Compliant and 100% Lead (Pb)-Free
Applications
l Portable Instruments
l Microprocessors and DSP Core supplies
l Cellular Telephones
l Wireless and DSL Modems
l Digital Cameras
l PC Cards
Pin Configurations
(TOP VIEW)
16 15 14 13
PGND 1
12 PVDD
PGND
PGND
FB
2
3
4
PGND
17
11 PVDD
10 PVDD
9 VDD
5678
WQFN-16L 3x3
DS8058-02 August 2007
www.richtek.com
1
1 page  
Preliminary
Typical Operating Characteristics
100
90
80
70
60
50
40
www.DataSheet4U.c3o0m
20
10
0
0
Efficiency vs. Output Current
VIN = 5V
VIN = 3.3V
VOUT = 1.8V, L = 3.3µH, COUT = 22µFx2
500
1000
1500
Output Current (mA)
2000
100
90
80
70
60
50
40
30
20
10
0
0
RT8058
Efficiency vs. Output Current
VIN = 5V
VIN = 3.3V
VOUT = 1.2V, L = 3.3µH, COUT = 22µFx2
500
1000
1500
Output Current (mA)
2000
Output Voltage vs. Outout Current
1.2000
1.1998
1.1996
1.1994
VIN = 5V
1.1992
1.1990
1.1988
1.1986
VIN = 3.3V
1.1984
1.1982
1.1980
0
250 500 750 1000 1250 1500 1750 2000
Outout Current (mA)
Output Voltage vs. Temperature
1.205
1.203
1.201
1.199
1.197
1.195
1.193
1.191
1.189
1.187
1.185
-50
-25
VIN = 3.6V
0 25 50 75
Temperature (°C)
100 125
Reference Voltage vs. Input Voltage
0.6010
0.6008
0.6006
0.6004
0.6002
0.6000
0.5998
0.5996
0.5994
0.5992
0.5990
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
Frequency vs. Temperature
1100
1050
1000
950
900
850
-50
-25
VIN = 3.6V, VOUT = 1.2V, IOUT = 0A
0 25 50 75
Temperature (°C)
100 125
DS8058-02 August 2007
www.richtek.com
5
5 Page 
Preliminary
RT8058
Short-Circuit Protection
At overload condition, current mode operation provides
cycle-by-cycle current limit to protect the internal power
switches. When the output is shorted to ground, the
inductor current will decays very slowly during a single
switching cycle. A current runaway detector is used to
monitor inductor current. As current increasing beyond
the control of current loop, switching cycles will be skipped
to prevent current runaway from occurring. If the FB voltage
www.DataShiseest4mU.aclolmer than 0.3V after the completion of soft-start
period, under voltage protection (UVP) will lock the output
to high-z to protect the converter. UVP lock can only be
cleared by recycling the input power.
Thermal Protection
If the junction temperature of RT8058 reaches certain
temperature (150°C), both converters will be disabled. The
RT8058 will be re-enabled and automatically initializes
internal soft start when the junction temperature drops
below 110°C.
Inductor Selection
For a given input and output voltage, the inductor value
and operating frequency determine the ripple current. The
ripple current ∆IL increases with higher VIN and decreases
with higher inductance.
ΔIL
=
VOUT
f × L
×
1−
VOUT
VIN
Having a lower ripple current reduces the ESR losses in
the output capacitors and the output voltage ripple. Highest
efficiency operation is achieved at low frequency with small
ripple current. This, however, requires a large inductor. A
reasonable starting point for selecting the ripple current
is ∆IL = 0.4(IMAX). The largest ripple current occurs at
the highest VIN. To guarantee that the ripple current stays
below a specified maximum, the inductor value should be
chosen according to the following equation :
L
=
f
×
VOUT
∆IL(MAX)
×
1 −
VOUT
VIN(MAX)
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High efficiency converters generally cannot
afford the core loss found in low cost powdered iron cores,
DS8058-02 August 2007
forcing the use of more expensive ferrite or mollypermalloy
cores. Actual core loss is independent of core size for a
fixed inductor value but it is very dependent on the
inductance selected. As the inductance increases, core
losses decrease. Unfortunately, increased inductance
requires more turns of wire and therefore copper losses
will increase.
Ferrite designs have very low core losses and are preferred
at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard”, which means that
inductance collapses abruptly when the peak design
current is exceeded. This result in an abrupt increase in
inductor ripple current and consequent output voltage ripple.
Do not allow the core to saturate!
Different core materials and shapes will change the size/
current and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and don' t radiate energy but generally cost more
than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price vs. size requirements and
any radiated field/EMI requirements.
CIN and COUT Selection
The input capacitance, CIN, is needed to filter the
trapezoidal current at the source of the top MOSFET. To
prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used. RMS
current is given by :
IRMS
= IOUT(MAX)
VOUT
VIN
VIN − 1
VOUT
This formula has a maximum at VIN = 2VOUT, where IRMS
= IOUT/2. This simple worst-case condition is commonly
used for design because even significant deviations do
not offer much relief. Note that ripple current ratings from
capacitor manufacturers are often based on only 2000
hours of life which makes it advisable to further derate the
capacitor, or choose a capacitor rated at a higher
temperature than required. Several capacitors may also
be paralleled to meet size or height requirements in the
design.
www.richtek.com
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8058.PDF ] | |
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